Analog signal measuring, generating or processing apparatus are usually equipped with manually operable controls such as rotary switches, potentiometers, verniers and the like each having appropriate front panel legends. Besides taking substantial panel and chassis space, these controls frequently do not provide the accuracy or resolution desired. Furthermore, the mechanical interface constrains the layout of electronic circuitry and makes remotely controlled and automatic measurements extremely difficult to implement.
One solution to the above-mentioned problems is shown in U.S. Pat. No. 3,629,845 which provides digital adjustment of the functions formerly adjusted manually by the operator. A parameter of a circuit to be controlled is displayed and manipulated by a digital logic circuit that is controlled by the operator from a digital incrementer on a control panel. The parameter may be incremented or decremented, but the determination and amount of each increment is fixed and without regard to circuit or instrument calibration.
Conventional electronic instrumentation, particularly measuring instruments, from time-to-time require calibration to compensate for changes in component values and characteristics and changes in operating environment, to accommodate different measurements by the same instrument and to perform many of the same measurements by several of the same instruments. Typically, prior art instruments employed manually adjusted variable resistors, capacitors, inductors and the like to maximize instrument performance under particular conditions for a specific measurement.